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Dry sump oil tank plug

My dry sump oil tank has one fitting in the lower half than needs to be plugged in my application (1700 BDR). What was in there was a large, headless, hex-drive plug, like a giant set-screw. The flange on the tank and the plug/screw each have a cross-hole, through which a cotter-pin is inserted, to keep the plug from moving. Problem is that this is a leak path for oil. Pictures (I don't know why the forum turns my pictures 90 degrees):

The fit of the threads is very loose. I know I could just wrap a bunch of pipe thread tape around the plug and put it in, or use pipe thread sealant from a tube. But neither of these seems like the right way to seal this hole. Seems like I'd want a bolt with a head on it, i.e. an oil drain plug, so I can torque it down, which would snug the threads up and help the tape or sealant to seal.

As best I can measure and guesstimate, the threads on the plug are M20-1.5. When I search that I do find oil pan drain plugs that have that thread size. They're not anodized aluminum as this plug is. Steel bolt in aluminum tank might corrode.

I would guess that all your fittings are on the tank are JIC i.e. AN, and that you need a 7/8-14 drain plug. A metric 20mm thread actually has a pitch of 2.5.
I would 2nd the use of a drain plug with an o-ring or sealing washer.
DaveW

I’ve been in touch and am slightly embarrassed to have sold a set of oil leaks (with a free Caterham thrown in for good measure), but this one at least should be straightforward to fix. My only worry with PTFE tape is that fragments might end up in the oil, but applied carefully should be fine. The original tank came from Dave Bean.

Stewart you've been great - very helpful. This was the biggest leak point, and likely the easiest to fix. I'm getting to know the car better through this work so no worries. The other leaks - around the pump, and front left engine, seem slower, so I'll likely live with those into next season and try to figure them out over time. The pump might be the adjusting screw, and I did buy a sealing washer to go on that, so we'll see if that helps. And the front left engine is likely the hoses that you had mentioned to me. Those look tough to get at. Wondering if other folks have experience with that on a BDR?

I have finally confirmed the thread size: 1/2" NPT. So I think the best solution is along the lines of what fastg says above: 1/2" NPT male to 6 AN male adapter, washer between adapter and tank, and a 6 AN cap. Now to order, likely from Summit Racing.